The mixed-phase relative rates approach for determining aerosol particle organic heterogeneous reaction kinetics is often performed utilizing mass spectral tracers as a proxy for particle-phase reactant concentration. However, this approach may be influenced by signal contamination from oxidation products during the experiment. In the current study, the mixed-phase relative rates technique has been improved by combining a positive matrix factor (PMF) analysis with electron ionization aerosol mass spectrometry (unit-mass resolution), thereby removing the influence of m/z fragments from reaction products on the reactant signals. To demonstrate the advantages of this approach, the heterogeneous reaction between OH radicals and citric acid (CA) was investigated using a photochemical flow tube coupled to a compact time-of-flight aerosol mass spectrometer (C-ToF-AMS). The measured heterogeneous rate constant (k(2)) of citric acid toward OH was (3.31 +/- 0.29) x10(-12) cm(3) molecule(-1) s(-1) at 298K and (30 +/- 3) % relative humidity (RH) and was several times greater than the results utilizing individual m/z fragments. This phenomenon was further evaluated for particulate-phase organophosphates (triphenyl phosphate (TPhP), tris-1,3-dichloro-2-propyl phosphate (TDCPP) and tris-2-ethylhexyl phosphate (TEHP)), leading to k(2) values significantly larger than previously reported. The results suggest that heterogeneous kinetics can be significantly underestimated when the structure of the products is highly similar to the reactant and when a non-molecular tracer is measured with a unit-mass resolution aerosol mass spectrometer. The results also suggest that the heterogeneous lifetime of organic aerosol in models can be overestimated due to underestimated OH uptake coefficients. Finally, a comparison of reported rate constants implies that the heterogeneous oxidation of aerosols will be dependent upon a number of factors related to the reaction system, and that a single rate constant for one system cannot be universally applied under all conditions.
Peroxy radical chemistry is the main component of tropospheric chemistry, which is critical for the understanding of essential tropospheric issues such as atmospheric cleansing capacity, photochemical ozone production and secondary organic aerosol formations. Field measurements of peroxy radical concentrations and related analysis with observation based model are the prominent steps to foster the current understanding of peroxy radical chemistry. This paper reviews the state of measurement techniques for peroxy radical, extensively revisits the previous field studies with direct measurements of peroxy radical, outlins the peroxy radical concentrations reported in previous field observations, summarizes the tests of photochemical mechanism with direct field measurement results and discusses the major scientific findings achieved so far. Finally, an outlook for the new directions in the study of atmospheric peroxy radical chemistry is proposed.
The architecture and performance of microbial desalination cell (MDC) have been significantly improved in the past few years. However, the application of MDC is still limited in a scope of small-scale (milliliter) reactors and high-salinity-water desalination. In this study, a large-scale (>10 L) stacked MDC packed with mixed ion-exchange resins was fabricated and operated in the batch mode with a salt concentration of 0.5 g/L NaCl, a typical level of domestic wastewater. With circulation flow rate of 80 mL/min, the stacked resin-packed MDC (SR-MDC) achieved a desalination efficiency of 95.8% and a final effluent concentration of 0.02 g/L in 12 h, which is comparable with the effluent quality of reverse osmosis in terms of salinity. Moreover, the SR-MDC kept a stable desalination performance (>9396) when concentrate volume decreased from 2.4 to 0.1 L (diluate/concentrate volume ratio increased from 1:1 to 1:0.04), where only 0.875 L of nonfresh water was consumed to desalinate 1 L of saline water. In addition, the SR-MDC achieved a considerable desalination rate (95.4 mg/h), suggesting a promising application for secondary effluent desalination through deriving biochemical electricity from wastewater.
A gyrotron capable of both frequency and power tuning is a promising coherent millimeter-THz wave source. A self-consistent nonlinear theory is applied to investigate the electron cyclotron interaction between electron beam and wave modes of axial nonfixed profiles in an extended W-band TE01 mode cylindrical cavity. It is revealed that tuning the magnetic field strength can excite electron cyclotron resonances on forward wave, backward wave, and even simultaneous on both waves, which makes the system operate under distinctive states, namely the gyrotron backward wave oscillation state and the gyromonotron state. In this paper, a W-band prototype gyrotron oscillator based on an extended cylindrical waveguide cavity is built, and the experiment test indicates that the system starts oscillation in a relative wide range of the operation parameters. The measured frequency spectrum reveals the system iteratively switches between the lower order instability axial modes, and it operates under nonstationary oscillation states. The experimental measurement of highest output power ~8 kW is consistent with the theoretical predictions. An optimized gyrotron circuit with efficiency exceeding 20% and tunable bandwidth over 10 GHz is also presented. The free oscillation behaviors revealed in this paper provide interesting guidance for developing tunable gyrotrons in millimeter-THz wave range.
A three-level trade-off analysis is proposed for decision making in environmental engineering under interval uncertainty, capable of providing both extreme and non-extreme decision alternatives at different risk levels for constraint and objective function violations. The essence of three-level trade-off analysis is the use of both modified interval linear programming and enhanced interval linear programming models to generate risk-based decision alternatives by qualitatively dividing the risk levels of the parameters in both the constraints and the objective function. The generated decision alternatives include two extremes, two appropriate values and one expected value, and two other non-extremes. The results of a numerical example and a real-world case study (Lake Qionghai Watershed, China) indicate that this procedure can support decision-making processes for stakeholders at different levels of risk to system benefits, within absolutely feasible and optimal solution spaces.
In China, booming tourism is considered to be a win-win solution to fight both ecosystem degradation and poverty in pastoral areas. However, whether this alternative livelihood can reduce pressure on rangeland and improve livelihood of indigenous peoples has not yet been explored. To examine tourism’s impacts on pastoral communities, we conducted field surveys at Inner Mongolia and Xinjiang and distributed questionnaires in 12 provinces including most of the grassland areas of China. On the basis of fieldwork and national survey data, we found that different types of operations have different impacts on livelihood and ecosystem in pastoral area. Pastoralists involved in tourism can increase the income of pastoral households during the summer tourism season, but that pastoralism still provides the main guarantee of a sustainable livelihood. However, along with the development of tourism, business enterprises from outside the pastoral area may replace local herders in tourism operations. As a result, a large area of rangeland may be lost to local herders, who only receive money if they rent their pastures or serve as laborers; unfortunately, many residents lack the training to perform better-paid roles. In addition, we found that pure tourism that replaces pastoralism does not necessarily protect the rangeland, as it brings a variety of environmental impacts and disrupts traditional use that the rangeland may be adapted to. On the basis of our findings, we recommend that tourism managed by local operators who also engage in pastoralism should become the main direction for economic development.